1. Field of the Invention
The present invention relates to a process for making a radial tire. A radial tire is much superior to a bias tire in steering property and enjoys a great demand in the public market. But the manufacturing process of a radial tire is more complicated than that of a bias tire and a lot of non-uniform and non-standardized radial tires have been manufactured. It is therefore an important problem for those concerned in the tire manufacturing industry to reduce the number of such defective products.
2. Description of the Prior Art
An example of a conventional process for making a radial tire will be briefly described hereunder. In the first step, as shown in FIG. 1, bead portion Ga, Ga of a cylindrically formed tire carcass assembly G comprising a carcass ply layer, bead portions and side wall rubbers are mounted to rims 1a, 1a of a pair of flanges 1, 1 of a radial tire building machine. Thereafter, as shown in FIG. 2, belt rings 2, 2 prepared beside the flanges 1, 1 approach each other to a given position and also both flanges 1, 1 approach each other while incorporating compressed air into the space surrounded by the flanges 1, 1 and the tire carcass assembly G. Thus, the tire carcass assembly G is expanded and transformed into a toroidal shape with the top Gb thereof being exposed through the gap between the edges of the belt rings 2, 2. Thereafter, as shown in FIG. 3, a plurality of belts 3, 3 and a tread cap 4 are laid over in turn in an endless form spanning between both of the belt rings 2, 2 and joined together with the operation of a pair of stitch rollers 5, 5. The belt rings 2, 2 are moved back to the stand-by position. Thereafter, stitch rollers 5, 5 are operated again, so that the lower surface of the lowest belt 3 and the lower surface of the side edges of the tread cap 4 are joined onto the upper surface of the tire carcass assembly G.
A green tire thus obtained, however, has such a drawback that the equatorial diameter is expanded with the approximately uniform expansion of the green tire in every direction by a shaping pressure added therein. If the equatorial diameter of a green tire is formed so as to fit the inner size of a vulcanizing metal mold, the equatorial diameter of the green tire becomes larger than that of the vulcanizing metal mold at the time of vulcanization when the vulcanizing metal mold is closed by applying a shaping pressure to the green tire. As a result, a part of the green tire is bitten between an upper mold and a lower one. Accordingly, there is employed such a measure as making the equatorial diameter of a green tire smaller by 6% to 7% than that of a vulcanizing metal mold so as to prevent the bite trouble. This measure, however, induces the increase of a dimensional difference between the cross sectional shape of a vulcanizing metal mold and that of a green tire at the portions other than the equatorial portion of a green tire. As a result, a big slip occurs among the structural members of a green tire at the vulcanization stage with the shaping pressure, thereby causing the non-uniformity of tires produced. Besides, as the belts 3, 3 and the tread cap 4 are joined onto the upper surface of the tire carcass assembly G which was transformed into nearly semicircular shape in cross section, the distance (see FIG. 3) from the upper surface of the tire carcass assembly G to the lower surface of the side edges of the belt 3 becomes large. As a result, the belt 3 and the tread cap 4 undergo great deformation when they are pressed by the stitch rollers 5, 5 and thereby wrinkles are often induced. Thus the uniformity of products becomes low.